Environmental toxins double risk of non-Hodgkin lymphoma, study finds

01 February 2008

Researchers funded in part by the Canadian Cancer Society have found that exposure to certain environmental contaminants may increase the risk of non-Hodgkin lymphoma.

Dr John Spinelli and his research team at the B.C. Cancer Agency collected blood samples from close to 900 BC residents – half with non-Hodgkin lymphoma (NHL) and half without. They found that the patients with NHL had much higher levels of environmental contaminants, specifically organochlorine pesticides and polychlorinated biphenyls (PCBs), in their blood than the cancer-free patients.

Individuals who had the highest total exposure to PCBs showed twice the risk for NHL compared to those with the lowest exposure. Furthermore, individuals with the highest levels of oxychlordane – a by-product of the pesticide chlordane – had 2.7 times the risk for developing NHL compared to those with the lowest exposure.

“We know that the incidence of non-Hodgkin lymphoma has been rising steadily for the past 30 years worldwide, but there hasn’t been clear evidence to explain the increase,” says Dr Spinelli. “Our study helps to provide answers to this puzzle by showing a strong link between these specific environmental contaminants and this particular type of cancer.”

Although the use of PCBs and organochlorine pesticides has been banned in Canada for decades, the chemicals are still used in many other parts of the world. In Canada today, PCBs are only allowed to be used as insulating fluid in existing electrical equipment. These kinds of contaminants have a very long half life, however, which means they may take decades or more to degrade, Dr Spinelli explains.

The reduction and elimination in the use of these chemicals explains the leveling off of NHL incidence rates in recent years, Dr Spinelli says. This can be expected if the chemicals had something to do with the increase in the disease initially.

Since environmental factors do not provide the full picture of NHL, the research team will now try to identify genetic factors that make individuals more susceptible to these contaminants. “In this way, we may be able to determine the mechanism by which contaminants increase the risk for lymphoma,” Dr Spinelli says, “and this knowledge may help to identify environmental risk factors earlier.”

Dr John Spinelli received approximately $554,000 from the Canadian Cancer Society over three years for work on the study.

In 2007, an estimated 6,800 Canadians will be diagnosed with non-Hodgkin lymphoma and 3,100 will die of it.